The present invention relates to an acoustic fluid machine, the machine utilizing fluctuations in pressure amplitude based on acoustic resonance.
In JP2006-266202A, there is an acoustic fluid machine in which a vibrating plate which reciprocates at high speed axially with a very small amplitude by driving sound source is provided on the inside of a larger-diameter base of an acoustic resonator, and a gas is taken into the acoustic resonator and discharged therefrom via a smaller-diameter upper end by virtue of pressure fluctuations within the acoustic resonator by reciprocation of the vibrating plate.
This acoustic fluid machine utilizes fluctuations in the pressure amplitude of standing acoustic waves generated by the phenomenon of resonance of a gas column inside the resonator by the piston when the piston is made to reciprocate axially with a very small amplitude, and comprises as an operating part only an actuator that reciprocates vibrating plate provided in the base of the acoustic resonator at high speed.
For reference, a typical structure of the acoustic fluid machine in JP2006-266202A will be described with reference to FIG. 5.
In the acoustic fluid machine, an actuator 32 is mounted in a larger-diameter portion at the lower end or the base of an acoustic resonator 31, and a valve device 33 is mounted in a smaller-diameter upper end of the acoustic resonator 31.
The acoustic resonator 31 has a resonant cavity 34 having a larger-diameter lower end and the diameter gradually decreases toward the top.
The actuator 32 also functions as a support, and includes a circular-plate piston 36 on the upper face thereof. The piston 36 is vibrated up and down by an appropriate vibration unit (not shown) via a reciprocation vibrating rod 35. The piston 36 is made of a light alloy and is fitted in the lower end of the resonant cavity 34. The outer circumference of the piston 36 has an annular groove 37 in which an O-ring 38 is fitted for sealing.
The acoustic resonator 31 has an outward flange 39 at the lower end. The outward flange 39 is disposed on the upper surface of the actuator 2, and the outward flange 39 and the actuator 32 are secured to each other by means of an appropriate number of bolts 40.
The valve device 33 is provided with an intake chamber 45 and a discharge chamber 49 that are arranged in line. The intake chamber 45 is equipped with an inlet 41 on one side of the valve device 33 and an intake hole 44 in the lower face of a bottom wall 42, with an inward check valve 43 for taking in external air, and the discharge chamber 49 is equipped with an outlet 46 on the other side of the valve device 33 and a discharge hole 48 in the upper face of the bottom wall 42, with an outward check valve 47 for discharging compressed air.
The inward and outward check valves 43 and 47 are formed from a reed valve or a rubber sheet valve made of, for example, a thin steel sheet. The valves 43, 47 are secured at one end to the lower side of the bottom of the intake chamber 45 and the upper side of the bottom of the discharge chamber 49, respectively. However, they may be of a ball type or any other type.
The valve-opening resistance of the outward check valve 47 is set so as to be considerably larger than that of the inward check valve 43.
The intake chamber 45 and the discharge chamber 49 are partitioned by a wall 50.
When the piston 36 reciprocates with a very small amplitude axially in the larger-diameter base at the lower end of the acoustic resonator 31 to allow the pressure amplitude within the acoustic resonator 31 to become a very small value, external air is taken in via the inlet 41, flows into the intake chamber 45, and is sucked into the acoustic resonator 31 via the intake hole 44 and the inward check valve 43. When the pressure amplitude within the acoustic resonator 31 becomes very small value, the air is discharged under compression from the acoustic resonator 31 via the discharge hole 48, the outward check valve 47, the discharge chamber 49 and the outlet 46.
Thus, the acoustic fluid machine has a very simple structure, has the advantage that a possibility of malfunction is very small, and can be used for various applications.
In the acoustic fluid machine described above, the flexible seal ring such as an O-ring is fitted in the annular groove in the outer circumferential surface of the piston in the acoustic resonator, the piston reciprocates axially with a very small amplitude at a sliding area of the seal ring in the acoustic resonator to generate sine waves thereby compressing the gas in the acoustic resonator.
However, in a usual acoustic fluid machine, as the amplitude of the seal ring is about 100-500 μm and the piston performs very small reciprocations at about 1000 times a second, only a certain portion of the seal ring bumps and wears locally, resulting in a leakage from the portion.
Therefore, the acoustic fluid machine performs badly and can not be used.
The seal ring inherently has frictional resistance, and the resistance and frictional heat increase when it is subjected to high-frequency vibration, affecting each of members harmfully, increasing load to the actuator as a sound-driving source, and decreasing the performance and durability.
When the seal ring is operated for a long time, it wears locally, bumps unevenly, or deteriorates, thereby causing heated gas to leak via the portion, making into performance poorer.